The present invention relates to a valve for a motor vehicle fuel tank for connection to a degassing circuit through which air and fuel vapor contained in the tank escape while the tank is being filled.
The degassing circuit communicates with the atmosphere via an activated carbon filter, also known as a xe2x80x9ccannisterxe2x80x9d, for the purpose of preventing fuel vapor being dumped into the atmosphere.
The valve needs to be opened while the tank is being filled so as to avoid impeding the flow of air and fuel vapor to the degassing circuit.
Nevertheless, it is desirable to prevent droplets of fuel being entrained into the degassing circuit while the vehicle is running since they might reach the activated carbon filter which would rapidly become saturated and thus lose its effectiveness.
German patent application DE-195 09 889 describes a motor vehicle tank degassing device for controlling the passage of fuel vapor to a cannister, the valve including a magnetizable element that can be moved under magnetic drive to open or to close the passage to the canister.
German patent application DE-40 12 368 describes a degassing device having a moving magnetizable element suitable for closing the passage to a cannister, with movement of the disk being controlled by means of an electromagnet and a spring.
Each of those two devices also includes a respective floating body that is separate from the magnetizable element and suitable for rising when the level of fuel in the tank rises, thereby closing the passage to the cannister at the end of tank filling.
The above-mentioned devices are relatively complex in structure, and in particular they comprise large numbers of parts.
A particular object of the present invention is to propose a novel valve which is capable firstly of providing effective ventilation of the tank while it is being filled and secondly of reducing the risk of liquid fuel reaching the degassing circuit while the vehicle is running.
Another object of the invention is to simplify the structure of the valve, in particular by reducing the number of its component parts.
The invention achieves this by the fact that the valve has a moving closure member and means that can be controlled from outside the tank to act on said closure member and bring it into a predetermined position when the vehicle is in a predetermined state, e.g. into a position in which the valve is completely or partially closed while the engine is running, the closure member being suitable for rising by floating on the surface of the fuel.
Advantageously, the means for acting on the closure member bring it into the open position while the tank is being filled.
The closure member can thus have a float function solely while the tank is being filled and the valve is open.
The means for acting on the closure member can advantageously include a coil that is excited by an electric current to exert an electromagnetic force on the closure member, the closure member then being magnetizable.
The coil can be excited electrically at the beginning of filling so as to create a magnetic field tending to cancel the effects of a permanent magnet.
Advantageously, in the absence of electrical excitation of the coil, the permanent magnet is suitable for holding the closure member in a high position for closing the valve.
In a particular embodiment, the closure member has a magnetizable metal part on top, e.g. a magnetizable metal ring, and the valve has a coil wound around a permanent magnet such that when the closure member is in the valve-closing position, the metal part is attracted by the permanent magnet sufficiently to hold the closure member in the closed position even though the coil is carrying no current.
The magnetic attraction of the metal part of the closure member to the permanent magnet can be interrupted when the coil is powered in such a manner as to create a magnetic field opposite to that of the permanent magnet, the closure member then returning under gravity to its open position.
The excitation of the coil which enables a magnetic field to be created that tends to cancel the effects of the permanent magnet at the time of filling can advantageously be caused to come into operation by removal of the filler cap from the tank.
In another implementation of the invention, the means for acting on the closure member make use of the energy of a fuel pump, which pump is advantageously the same as the pump used for delivering fuel to the injectors of the engine.
When the engine is running, the fuel pump delivers fuel at relatively high pressure and the energy thereof is advantageously used for bringing the closure member into the closed position.
When the engine is switched off, this energy ceases to be supplied and the closure member can return to an open position.
The valve can include a nozzle squirting a jet of fuel beneath the closure member, said jet tending to bring it into a valve closure position where it closes access to the degassing circuit.
In a variant, the means for acting on the closure member can comprise a diaphragm suitable for inflating under the effect of fuel being delivered under pressure.
In a preferred embodiment, the closure member is suitable for closing the degassing circuit in the event of the vehicle accidentally rolling over.
The invention also provides a motor vehicle fuel tank fitted with a valve as specified above.
Other characteristics and advantages of the present invention will appear on reading the following detailed description of three non-limiting embodiments of the invention, and on examining the accompanying drawings, in which: